Combustor for exhaust gas treatment

ABSTRACT

The present invention provides a burner for use in a combustion-type waste gas treatment system for combusting waste gases emitted from semiconductor manufacturing system, particularly, a deposition gas containing SiH 4  and a halogen-base gas, simultaneously at a high efficiency of destruction, making it difficult for a powder of SiO 2  to be attached and deposited, performing a low-NOx combustion, and maintaining a desired level of safety. The combustion-type waste gas treatment system has a flame stabilizing zone ( 15 ), which is open toward a combustion chamber ( 11 ), surrounded by a peripheral wall ( 12 ), and closed by a plate ( 14 ) remotely from the combustion chamber. A waste gas, an auxiliary combustible agent, and air are introduced into and mixed with each other in the flame stabilizing zone ( 15 ), and the mixed gases are ejected toward the combustion chamber ( 11 ) perpendicularly to the plate ( 14 ).

TECHNICAL FIELD

The present invention relates to a waste gas treating burner for use ina combustion-type waste gas treatment system for combusting harmfulwaste gases such as a deposition gas containing SiH₄ and a halogen-basegas (CHF₃, C₂F₆, CF₄, etc.), which are emitted from semiconductormanufacturing system.

BACKGROUND ART

Semiconductor manufacturing system emits harmful waste gases such as adeposition gas containing SiH₄ and a halogen-base gas (CHF₃, C₂F₆, CF₄,etc.), which should not be discharged directly into the atmosphere. Itis therefore the general practice in the art to introduce such harmfulwaste gases into an abatement system where the waste gas is detoxifiedby way of combustion. According to the general waste gas treatmentsystem, an auxiliary combustible gas is used to produce flames in afurnace for thereby combusting the waste gases.

In the combustion-type waste gas treatment system, the auxiliarycombustible gas is usually in the form of a combination of a fuel gassuch as hydrogen, a town gas, LPG, etc. and an oxidizing agent such asoxygen or air. Most of the operating cost of the combustion-type wastegas treatment system constitutes expenses required by the consumption ofthe fuel gas and the oxidizing agent. One of the indicators of theperformance of combustion-type waste gas treatment system is how muchharmful waste gases can be destroyed with a high efficiency with a smallamount of auxiliary combustible gas. It is known in the art that whenthe deposition gas containing SiH₄ is thermally destroyed, a powder ofSiO₂ is generated which tends to be deposited in the combustion chamberand cause various troubles to the combustion chamber. Consequently, adesign approach to make the combustion chamber resistant to thedeposition therein of a powder of SiO₂ is also an important element inevaluating the combustion-type waste gas treatment system.

One general burner for use in conventional combustion-type waste gastreatment system is shown in FIGS. 28 and 29 of the accompanyingdrawings. As shown in FIGS. 28 and 29, the burner has a waste gas nozzle2 defined centrally in the ceiling of a cylindrical combustion chamber1, for introducing a waste gas A to be treated into the combustionchamber 1, and a plurality of auxiliary combustible gas nozzles 3defined in the ceiling of the cylindrical combustion chamber 1 aroundthe waste gas nozzle 2, for introducing an auxiliary combustible gas Binto the combustion chamber 1, with a combustion gas outlet 4 integrallyjoined to the lower end of the combustion chamber 1. The auxiliarycombustible gas B ejected from the auxiliary combustible gas nozzles 3produces flames in a circular pattern. While the waste gas A passescentrally through the circular pattern of flames, the waste gas A ismixed with and combusted by the flames, emitting a combustion exhaustgas which is discharged out of the combustion chamber 1 through thecombustion gas outlet 4.

With the conventional burner, however, since the flames produced by theauxiliary combustible gas are formed in front of the auxiliarycombustible gas nozzles, the waste gas discharged forward from the wastegas nozzle which is positioned inwardly of the auxiliary combustible gasnozzles is not necessarily sufficiently mixed with the flames, and hencethe efficiency of destruction of the waste gas is not sufficiently high.In order to increase the efficiency of destruction, it is necessary toincrease the amount of auxiliary combustible gas to produce largeflames, which allow the waste gas to be easily combusted and destroyed.However, the amount of auxiliary combustible gas, which does notcontribute to the destruction of the waste gas is also increased,resulting in an increase in the operating cost of the combustion-typewaste gas treatment system.

When a SiH₄ gas is destroyed by way of oxidization, a produced powder ofSiO₂ is attached to and deposited on wall surfaces where the exhaust gasflows slowly. If the concentration of SiH₄ in the waste gas is high,then the powder of SiO₂ is produced and deposited in an increasedquantity on the wall surfaces. In worst cases, an auxiliary combustiblegas may not be continuously combusted, and it may be necessary to shutoff the combustion-type waste gas treatment system for removal of thedeposited powder.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above difficulties.It is an object of the present invention to provide a burner for use ina combustion-type waste gas treatment system which is capable ofdestructing waste gases, particularly, a deposition gas containing SiH₄and a halogen-base gas, from a semiconductor fabrication facilitysimultaneously at a high efficiency of destruction, making it difficultfor a powder of SiO₂ to be attached and deposited, performing a low-NOxcombustion, and maintaining a desired level of safety.

According to the present invention, there is provided a burner fortreating a waste gas, characterized in that a flame stabilizing zone isopen toward a combustion chamber, surrounded by a peripheral wall, andclosed by a plate remotely from the combustion chamber, and a waste gas,an auxiliary combustible agent, and air are introduced into and mixedwith each other in the flame stabilizing zone, and the mixed gases areejected toward the combustion chamber perpendicularly to the plate.Preferably, the plate has, defined therein, a waste gas flame hole forejecting the waste gas toward the flame stabilizing zone and anauxiliary combustible gas flame hole for ejecting the auxiliarycombustible gas, and the peripheral wall of the flame stabilizing zonehas an air ejection nozzle arranged to eject the air substantiallycircumferentially to produce a swirling flow.

The waste gas including a deposition gas and a halogen-base gas, theauxiliary combustible agent, and the air are introduced into the flamestabilizing zone, which is open toward the combustion chamber, andsufficiently mixed with each other. The mixed gases remain sufficientlymixed without being dispersed, and are ejected toward the combustionchamber perpendicularly to the plate. Combustion flames produced in thecombustion chamber become elongate flames, expanding a high-temperatureregion downstream to increase the period of time in which the waste gasremains in the high-temperature region. Therefore, the waste gas is wellcombusted with a high efficiency of destruction, and a powder of SiO₂,which is produced, is efficiently discharged by a flow of combustiongas.

The air ejected substantially circumferentially from the peripheral wallproduces a strong swirling flow. The swirling flow has a vortex centerof the swirling air and a free vortex region around the vortex center.Since the flame holes for the waste gas and the auxiliary combustiblegas are defined in the plate, the waste gas and the auxiliarycombustible gas which are ejected from the flame holes are introducedinto the free vortex region and engulfed by the swirling air flow. Thewaste gas and the auxiliary combustible gas, which are ejected from theflame holes, are sheared due to changed in the speed of the swirling airflow by the free vortex region of the swirling air flow, andsufficiently mixed with the air, and the mixture of the waste gas, theauxiliary combustible gas, and the air produces swirling flames. Becausethe auxiliary combustible gas and the air are combusted after beingmixed in the swirling air flow, they produce pre-mixed flames to achievea low-NOx combustion. Since the auxiliary combustible agent and the airare mixed in the flame stabilizing zone, the auxiliary combustible agentis not ignited in the gas chamber, making the burner highly safe, evenwhen the peripheral wall of the flame stabilizing zone is heated by theflames.

Preferably, a second auxiliary combustible gas flame hole for ejectingthe auxiliary combustible gas is defined in the peripheral wall of theflame stabilizing zone downstream of the air ejection nozzle in an axialdirection of the flame stabilizing zone.

Flames produced by the auxiliary combustible gas are positioneddownstream of the second auxiliary combustible gas flame hole, and arecombined flames from the primary combustion, producing elongate flames.The elongate flames expand a high-temperature region downstream toincrease the period of time in which the waste gas remains in thehigh-temperature region. By thus expanding the flame-inducedhigh-temperature region downstream, the halogen-base waste gas inparticular can fully be destroyed.

The air ejection nozzle preferably comprises air ejection nozzles in aplurality of groups divided along the axial direction of the flamestabilizing zone.

When the air is divided in a plurality of groups and supplied to theflame stabilizing zone, the amount of air ejected from each of thegroups is small. At the inlet of the flame stabilizing zone, the amountof air required to combust the auxiliary combustible gas isinsufficient, producing fuel-rich flames, suppressing the generation ofNOx. At the outlet of the flame stabilizing zone, a sufficient amount ofair is supplied to produce fuel-lean flames, causing a low-NOxcombustion. Flames produced by the air ejected from the air ejectionnozzles in the plural groups become elongate flames. The elongate flamesexpand a high-temperature region downstream to increase the period oftime in which the waste gas remains in the high-temperature region, thusfully destructing the halogen-base waste gas in particular.

The flame stabilizing zone preferably is of a cylindrical shape. If anair ejection nozzle for ejecting air substantially circumferentially iscombined with the flame stabilizing zone, then a swirling air flow caneasily be produced in the flame stabilizing zone.

In a burner according to a second aspect of the present invention, asecond flame stabilizing zone is disposed downstream in the axialdirection of the flame stabilizing zone, and has, defined in aperipheral wall thereof, a second auxiliary combustible gas flame holefor ejecting a second auxiliary combustible gas, and a combustionchamber is disposed downstream of the second auxiliary combustible gasflame hole in an axial direction of the second flame stabilizing zone.

With the above arrangement, primary pre-mixed fuel-lean flames areproduced downstream of the flame stabilizing zone, and then theauxiliary combustible gas is ejected from the second flame stabilizingzone to produce secondary high-temperature low-oxygen flames downstreamthereof. Therefore, a deposition gas containing SiH₄ and a halogen-basegas can simultaneously be destroyed with a high efficiency, and a powderof SiO₂, which is produced, can efficiently be discharged by a flow ofcombustion gas. Consequently, the powder of SiO₂ is prevented from beingdeposited in the combustion chamber.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-sectional view showing a first embodimentof the present invention;

FIG. 2 is a cross-sectional view taken along line I—I of FIG. 1;

FIG. 3 is a longitudinal cross-sectional view showing a modification ofthe first embodiment of the present invention;

FIG. 4 is a cross-sectional view taken along line II—II of FIG. 3;

FIG. 5 is a longitudinal cross-sectional view showing anothermodification of the first embodiment of the present invention;

FIG. 6 is a cross-sectional view taken along line III—III of FIG. 5;

FIG. 7 is a longitudinal cross-sectional view showing a secondembodiment of the present invention;

FIG. 8 is a cross-sectional view taken along line I—I of FIG. 7;

FIG. 9 is a cross-sectional view taken along line II—II of FIG. 7;

FIG. 10 is a longitudinal cross-sectional view showing a modification ofthe second embodiment of the present invention;

FIG. 11 is a cross-sectional view taken along line III—III of FIG. 10;

FIG. 12 is a cross-sectional view taken along line IV—IV of FIG. 10;

FIG. 13 is a longitudinal cross-sectional view showing anothermodification of the second embodiment of the present invention;

FIG. 14 is a cross-sectional view taken along line V—V of FIG. 13;

FIG. 15 is a cross-sectional view taken along line VI—VI of FIG. 14;

FIG. 16 is a longitudinal cross-sectional view showing a thirdembodiment of the present invention;

FIG. 17 is a cross-sectional view taken along line I—I of FIG. 16;

FIG. 18 is a cross-sectional view taken along line II—II of FIG. 16;

FIG. 19 is a longitudinal cross-sectional view showing a fourthembodiment of the present invention;

FIG. 20 is a cross-sectional view taken along line III—III of FIG. 19;

FIG. 21 is a cross-sectional view taken along line IV—IV of FIG. 19;

FIG. 22 is a longitudinal cross-sectional view showing a fifthembodiment of the present invention;

FIG. 23 is a longitudinal cross-sectional view showing a sixthembodiment of the present invention;

FIG. 24 is a longitudinal cross-sectional view showing a seventhembodiment of the present invention;

FIG. 25 is a longitudinal cross-sectional view showing an eighthembodiment of the present invention;

FIG. 26 is a longitudinal cross-sectional view showing a ninthembodiment of the present invention;

FIG. 27 is a longitudinal cross-sectional view showing a tenthembodiment of the present invention;

FIG. 28 is a longitudinal cross-sectional view showing a conventionalexample; and

FIG. 29 is a cross-sectional view taken along line VII—VII of FIG. 28.

BEST MODE FOR CARRYING OUT THE INVENTION

A first aspect of the present invention will be described below withreference to FIGS. 1 through 6.

FIGS. 1 and 2 show a first embodiment of the present invention. Acombustion chamber 11 is surrounded by a furnace wall 10. The combustionchamber 11 is confronted to a flame stabilizing zone 15, which issurrounded by a peripheral wall 13 defined by an inner peripheralsurface of a cylindrical body 12 and closed by a plate 14. Thecylindrical body 12 is integrally formed with the plate 14.

In the plate 14, there are defined a plurality of (four as shown) wastegas chambers 20 for holding and guiding a waste gas A to be treatedwhich is mainly composed of nitrogen and contains a halogen-base gasemitted from a semiconductor fabrication facility, for example, and aplurality of (four as shown) auxiliary combustible gas chambers 21 forholding and guiding an auxiliary combustible gas B which is a fuel gassuch as hydrogen, a town gas, LPG, etc. An air chamber 22 for holdingand guiding air C is defined in the cylindrical body 12, which extendsfrom the plate 14.

The plate 14 has, defined in a lower surface thereof, a plurality ofwaste gas flame holes 23 extending from the waste gas chambers 20 andopening toward the flame stabilizing zone 15, and a plurality ofauxiliary combustible gas flame holes 24 providing communication betweenthe auxiliary combustible gas chambers 21 and the flame stabilizing zone15. The waste gas flame holes 23 and the auxiliary combustible gas flameholes 24 are arranged in a doughnut-shaped pattern. The doughnut-shapedpattern means that the auxiliary combustible gas flame holes 24 aredisposed adjacent to the waste gas flame holes 23 in a substantiallycircumferential pattern substantially around the center of the plate 14that defines the flame stabilizing zone. In the present embodiment, thewaste gas flame holes 23 and the auxiliary combustible gas flame holes24 are positioned alternately with each other on an annular shape. Theannular shape is in same position with a free vortex region of aswirling air flow, in which a high speed region of the swirling air flowis formed, as described later on. The inner peripheral wall 13 of thecylindrical body 12 has a plurality of air ejection nozzles 25 providingcommunication between the air chamber 22 and the flame stabilizing zone15. The air ejection nozzles 25 extend substantially tangentially to thecircumferential surface of the flame stabilizing zone 15 for producingand ejecting a swirling flow of air C substantially circumferentiallytoward the flame stabilizing zone 15 (see FIG. 2).

The cylindrical body 12 also has a conical surface 12 a extendingconically from the peripheral wall 13 and joined to a side surface ofthe combustion chamber 11, partly making up the combustion chamber 11. Acombustion gas outlet 30 is integrally joined to the lower end of thecombustion chamber 11.

Operation of the present embodiment will be described below.

The air C is guided into and held by the air chamber 22, and ejectedsubstantially circumferentially as a strong swirling flow from the airejection nozzles 25 defined in the inner circumferential surface of thecylindrical body 12 into the flame stabilizing zone 15. The waste gas Ais guided into and held by the waste gas chambers 20, and ejected fromthe waste gas flame holes 23 defined in the lower surface of the plate14 into the flame stabilizing zone 15. The auxiliary combustible gas Bis guided into and held by the auxiliary combustible gas chambers 21,and ejected from the auxiliary combustible gas flame holes 24 defined inthe lower surface of the plate 14 into the flame stabilizing zone 15.After having been ejected from the flame holes, the auxiliarycombustible gas B is immediately combined with the waste gas A ejectedfrom the adjacent holes, and then mixed with the swirling air flow. Whenignited by an ignition source, not shown, the mixed gases produceswirling flames along the inner circumferential surface of thecylindrical body 12.

The air ejected substantially circumferentially from the peripheral wallproduces a strong swirling flow. The swirling flow has a vortex centertherein swirling together with the swirling flow and a doughnut-shapefree vortex region around the vortex center with the flow speed beinglower toward the outer edge of the doughnut-shape free vortex zone.Since the flame holes for the waste gas A and the auxiliary combustiblegas B are defined in the lower surface of the plate 14 in an annularshape in same position with a free vortex region, the waste gas A andthe auxiliary combustible gas B are ejected into the free vortex regionand engulfed by the swirling air flow. These gases are sheared due tochanges in the speed of the swirling air flow, and sufficiently mixedwith the air C. The mixture of the waste gas A, the auxiliarycombustible gas B, and the air C produces swirling flames. Because themixture produces flames after the waste gas A is sufficiently mixed inits entirety with the auxiliary combustible gas B and the air C, thewaste gas A is fully exposed to the flames and progressively destroyedby way of combustion with a high efficiency of destruction.

Although the auxiliary combustible gas B and the air C are separatelyblown into the flame stabilizing zone 15, since the waste gas A iscombusted after it is mixed with the auxiliary combustible gas A and theair C, pre-mixed flames are produced to achieve a low-NOx combustion.Pre-mixed flames are produced only when a fuel gas is sufficiently mixedwith air prior to combustion, and can be achieved when the fuel gas isejected from positions on the doughnut-shape pattern on the plate intothe free vortex region where the swirling air flow has a high speed, asis the case with the present invention. Inasmuch as the auxiliarycombustible gas B which is the fuel gas and the air C are mixed witheach other in the flame stabilizing zone, the auxiliary combustible gasB is not ignited in the auxiliary combustible gas chambers 21, makingthe burner highly safe, even if the cylindrical body is heated by theflames.

The air ejected from the air ejection nozzles 25 into the combustionchamber 11 cools the cylindrical body 12 as follows: While the swirlingflames heat the cylindrical body 12, it is necessary to cool thecylindrical body 12 to prevent its temperature from exceeding theheat-resistance temperature of the material of the cylindrical body 12for keeping combustion. The air ejected from the air ejection nozzles 25into the combustion chamber 11 acts to cool the surface of theperipheral wall 13 while mixing with the waste gas A and the auxiliarycombustible gas B and swirling in the flame stabilizing zone 15.

FIGS. 3 and 4 show a modification of the first embodiment of the presentinvention. According to this modification, the inside diameter of thecylindrical body 12 and the inside diameter of the combustion chamber 11in the first embodiment are made substantially the same as each other.The conical surface 12 a, which interconnects the peripheral wall 13 ofthe cylindrical body 12 and the side surface of the combustion chamber11 according to the first embodiment is replaced with a cylindricalsurface 12 b. With this structure, the diameter of the swirling flowremains substantially the same to the outlet, maintaining a goodswirling flow from the flame stabilizing zone to the outlet, so that anystagnant flow regions are eliminated and the mixing of the waste gas andthe swirling flames is promoted to increase the efficiency ofdestruction of the waste gas.

In this modification, there are two auxiliary combustible gas chambers21 and two auxiliary combustible gas flame holes 24, with the auxiliarycombustible gas flame holes 24 being positioned adjacent to the fourwaste gas flame holes 23, i.e., between the respective pairs of the fourwaste gas flame holes 23. With this arrangement, the primary auxiliarycombustible gas B is sufficiently mixed with the waste gas A, which isejected from adjacent positions.

FIGS. 5 and 6 show another modification of the first embodiment of thepresent invention. In this modification, the air chamber 22 defined inthe cylindrical body 12 extends substantially the full length in theaxial direction of the peripheral wall 13 of the cylindrical body 12.The air ejection nozzles 25 which provide communication between the airchamber 22 and the flame stabilizing zone 15 are provided in four at agroup in a circumferential surface. Specifically, the air ejectionnozzles 25 are provided in three groups including a first group 25 adefined in the peripheral wall closely to the plate, a second group 25 bsubstantially at the center in the longitudinal direction of theperipheral wall, and a third group 25 c defined in the peripheral wallat a position facing the combustion chamber. A combustion gas outlet 30is integrally joined to the lower end of the combustion chamber 11.

Operation of the present modification will be described below.

The air ejected from the air chamber 22 into the flame stabilizing zone15 is divided into three groups spaced along the axial direction of theperipheral wall 13. Usually, the total amount of supplied air is severalor several tens times the amount of auxiliary combustible gas. When theair is divided into three stages along the axial direction and suppliedto the flame stabilizing zone, the amount of air ejected from each ofthe groups is smaller than when the air is not divided, promoting themixing of the air, the exhaust gas, and the auxiliary combustible gas toincrease the efficiency of destruction. The amount of air ejected fromthe air ejection nozzles 25 a, 25 b in the first and second groups isnot large enough to combust all the fuel gas, producing fuel-rich flamesin the flame stabilizing zone to suppress the generation of NOx. Whenair is supplied from the third group of air ejection nozzles 25 c, thesufficient amount of air is supplied to the fuel gas, producingfuel-lean flames to perform a low-NOx combustion.

Flames produced by the air ejected from the third group of air ejectionnozzles 25 c occur downstream of the air ejection nozzles 25 c.Therefore, the flames become elongate frames, expanding thehigh-temperature region downstream to increase the period of time inwhich the waste gas remains high in temperature. With theflame-generated high-temperature region being expanded downstream, thehalogen waste gas can fully be destroyed. The air ejection nozzles inthe groups may not necessarily eject all air in a manner to produce aswirling air flow toward the flame stabilizing zone. For example, thethird group of air ejection nozzles may eject air simply downstream,rather than tangentially to the circumferential surface, or may ejectair toward the center of the flame stabilizing zone to cause turbulenceswith the waste gas and to be mixed with the waste gas.

FIGS. 7, 8, and 9 show a second embodiment of the present invention. Acombustion chamber 11 surrounded by a furnace wall 10 is confronted by aflame stabilizing zone 15, which is surrounded by a peripheral wall 13defined by an inner circumferential surface of a cylindrical body 12 andclosed by a plate 14. The cylindrical body 12 is integrally formed withthe plate 14. In the plate 14, there are defined a plurality of (four asshown) waste gas chambers 20 for holding and guiding a waste gas A to betreated which is mainly composed of nitrogen and contains a halogen-basegas emitted from a semiconductor fabrication facility, for example, anda plurality of (four as shown) first auxiliary combustible gas chambers21 a for holding and guiding a primary auxiliary combustible gas B1which is a fuel gas such as hydrogen, a town gas, LPG, etc. An airchamber 22 for holding and guiding air C and a second auxiliarycombustible gas chamber 21 b for holding and guiding a secondaryauxiliary combustible gas B2 which is a fuel gas are defined in thecylindrical body 12 which extends from the plate 14. The secondauxiliary combustible gas chamber 21 b is positioned closer to thecombustion chamber than the air chamber, i.e., downstream of the airchamber, in the axial direction of the flame stabilizing zone.

The plate 14 has, defined in a lower surface thereof, a plurality ofwaste gas flame holes 23 extending from the waste gas chambers 20 andopening toward the flame stabilizing zone 15, the waste gas flame holes23 being smaller in diameter than the flame stabilizing zone 15, and aplurality of first auxiliary combustible gas flame holes 24 a providingcommunication between the first auxiliary combustible gas chambers 21 aand the flame stabilizing zone 15, the waste gas flame holes 23 and thefirst auxiliary combustible gas flame holes 24 a being arranged in adoughnut-shaped pattern. The doughnut-shaped pattern means that thefirst auxiliary combustible gas flame holes 24 a are disposed adjacentto the waste gas flame holes 23 in a substantially annular shapesubstantially around the center of the plate that defines the flamestabilizing zone. In the present embodiment, the waste gas flame holes23 and the first auxiliary combustible gas flame holes 24 a arepositioned alternately with each other, and the annular shape is in sameposition with a free vortex region where a swirling air flow has a highspeed, as described later on.

The inner peripheral wall 13 of the cylindrical body 12 has a pluralityof air ejection nozzles 25 providing communication between the airchamber 22 and the flame stabilizing zone 15, and a plurality of secondauxiliary combustible gas flame holes 24 b positioned closer to thedownstream combustion chamber than the air ejection nozzles 25 in theaxial direction of the flame stabilizing zone. The air ejection nozzles25 extend substantially tangentially to the circumferential surface ofthe flame stabilizing zone 15 for producing and ejecting a swirling flowof air C substantially circumferentially toward the flame stabilizingzone 15. The second auxiliary combustible gas flame holes 24 b arearranged to eject a secondary auxiliary combustible gas B2 toward thecenter of the flame stabilizing zone 15.

Operation of the present embodiment will be described below.

The air C is guided into and held by the air chamber 22, and ejectedsubstantially circumferentially as a strong swirling flow from the airejection nozzles 25 defined in the inner circumferential surface of thecylindrical body 12 into the flame stabilizing zone 15. The waste gas Ais guided into and held by the waste gas chambers 20, and ejected fromthe waste gas flame holes 23 defined in the lower surface of the plate14 into the flame stabilizing zone 15. The primary auxiliary combustiblegas B1 is guided into and held by the first auxiliary combustible gaschambers 21 a, and ejected from the first auxiliary combustible gasflame holes 24 a defined in the lower surface of the plate 14 into theflame stabilizing zone 15. The waste gas A and the primary auxiliarycombustible gas B1 which are ejected are mixed with the swirling airflow. When ignited by an ignition source, not shown, the mixed gasesproduce swirling flames, which are primary flames, along the innercircumferential surface of the cylindrical body 12. The flow rate of theprimary auxiliary combustible gas B1 is smaller than a theoreticalequivalent to the flow rate of the air C, so that the produced primaryflames are fuel-lean combustion flames characterized by the lean fuel.

The air ejected substantially circumferentially from the peripheral wallproduces a strong swirling flow. The swirling flow has a vortex centerswirling together with the swirling flow and a doughnut-shape freevortex region around the vortex center with the flow speed being lowertoward the outer edge of the doughnut-shape free vortex region. Sincethe flame holes for the waste gas A and the primary auxiliarycombustible gas B1 are defined in the lower surface of the plate 14 inan annular shape in same position with a free vortex region, the wastegas A and the primary auxiliary combustible gas B1 are ejected into thefree vortex region and engulfed by the swirling air flow. These gasesare sheared due to changes in the speed of the swirling air flow, andsufficiently mixed with the air C. The mixture of the waste gas A, theprimary auxiliary combustible gas B1, and the air C produces swirlingfuel-lean flames and causes a primary combustion. Although the primaryauxiliary combustible gas B1 and the air C are separately blown into theflame stabilizing zone 15, since the waste gas is combusted after it ismixed with the primary auxiliary combustible gas and the air, pre-mixedflames are produced. Pre-mixed flames are produced only when a fuel gasis sufficiently mixed with air prior to combustion, and can be achievedwhen the fuel gas is ejected from positions on the doughnut-shapepattern on the plate into the free vortex region where the swirling airflow has a high speed, as is the case with the present invention.Pre-mixed flames cause a low-NOx combustion if they are fuel-leanflames. The pre-mixed flames produced in the present embodiment areflames where the fuel is lean, they cause a low-NOx combustion.

Then, the secondary auxiliary combustible gas B2 is ejected from thesecond auxiliary combustible gas flame holes 24 b into the swirlingflames as primary flames at the center of the flame stabilizing zone.The secondary auxiliary combustible gas B2 is well mixed with theprimary flames due to a shearing action of the swirling primary flameflow, and oxidized by oxygen remaining in the primary flames, causing asecondary combustion. Since the concentration of the oxygen remaining inthe primary flames is much lower than the concentration of oxygencontained in the air, a low-oxygen-concentration combustion takes placein the secondary combustion. In the low-oxygen-concentration combustion,NOx is produced in a small quantity, causing a low-NOx combustion. Theflames produced by the secondary combustion are positioned downstream ofthe second auxiliary combustible gas flame holes 24 b, and becomeelongate frames, expanding the high-temperature region downstream toincrease the period of time in which the waste gas remains high intemperature. With the flame-generated high-temperature region beingexpanded downstream, the halogen waste gas can fully be destroyed.

While the low-NOx combustion is being achieved, all the waste gas A issufficiently mixed with the primary auxiliary combustible gas B1, thesecondary auxiliary combustible gas B2, and the air C due to theswirling air flow, and then produces downstream elongate flames. Thewaste gas A is fully exposed to the flames and progressively destroyedby way of combustion with a high efficiency of destruction.

Inasmuch as the primary and secondary auxiliary combustible gases B1, B2which are the fuel gas and the air C are mixed with each other in theflame stabilizing zone, the auxiliary combustible gases are not ignitedin the first and second auxiliary combustible gas chambers 21 a, 21 b,making the burner highly safe, even if the cylindrical body is heated bythe flames. In the present embodiment, when the air C is suppliedcircumferentially to the air chamber 22, the air C swirls in the airchamber 22, uniformly cooling the air chamber 22 to prevent thecylindrical body from being heated. Similarly, when the secondaryauxiliary combustible gas B2 is supplied circumferentially to the secondauxiliary combustible gas chamber 21 b, the secondary auxiliarycombustible gas B2 swirls in the second auxiliary combustible gaschamber 21 b, uniformly cooling the second auxiliary combustible gaschamber 21 b.

FIGS. 10, 11, and 12 show a modification of the second embodiment of thepresent invention. According to this modification, the inside diameterof the cylindrical body 12 and the inside diameter of the combustionchamber 11 in the second embodiment are made substantially the same aseach other. The conical surface 12 a, which interconnects the peripheralwall 13 of the cylindrical body 12 and the side surface of thecombustion chamber 11, is replaced with a cylindrical surface 12 b. Withthis structure, the diameter of the swirling flow remains substantiallythe same to the outlet, maintaining a good swirling flow from the flamestabilizing zone to the outlet, so that any stagnant flow regions areeliminated and the mixing of the waste gas and the swirling flames ispromoted to increase the efficiency of destruction of the waste gas. Inthis modification, there are two primary auxiliary combustible gaschambers 21 a and two primary auxiliary combustible gas flame holes 24a, with the primary auxiliary combustible gas flame holes 24 a beingpositioned adjacent to the four waste gas flame holes 23, i.e., betweenthe respective pairs of the four waste gas flame holes 23. With thisarrangement, the primary auxiliary combustible gas B1 is sufficientlymixed with the waste gas A, which is ejected from adjacent positions ofholes.

FIGS. 13, 14, and 15 show another modification of the second embodimentof the present invention. In this modification, the air chamber 22defined in the cylindrical body 12 extends in the axial direction of theperipheral wall 13 of the cylindrical body 12. The air ejection nozzles25, which provide communication between the air chamber 22 and the flamestabilizing zone 15, are provided in four at a group in acircumferential surface. Specifically, the air ejection nozzles 25 areprovided in three groups including a first group 25 a defined in theperipheral wall closely to the plate, a second group 25 b substantiallyat the center in the longitudinal direction of the peripheral wall, anda third group 25 c defined in the peripheral wall at a position close tothe combustion chamber. A combustion gas outlet 30 is integrally joinedto the lower end of the combustion chamber 11. In this modification, thesecond auxiliary combustible gas flame holes 24 b are arranged to ejectthe secondary auxiliary combustible gas slightly downward.

In the present modification, the air ejected from the air chamber 22into the flame stabilizing zone 15 is divided into three groups spacedalong the axial direction of the peripheral wall 13. This action is thesame as with the modification shown in FIGS. 5 and 6.

In the above modifications, the burner may have a single auxiliarycombustible gas flame hole 24 or a single first auxiliary combustiblegas flame hole 24 a, which may be disposed between either pair of wastegas flame holes 23.

Alternatively, the burner may have a single waste gas flame hole 23 anda single auxiliary combustible gas flame hole 24 or a single firstauxiliary combustible gas flame hole 24 a, which may be positioned on acircular shape pattern substantially around the center of the flamestabilizing zone.

Further alternatively, the burner may have a single waste gas flame hole23 and two auxiliary combustible gas flame holes 24 or two firstauxiliary combustible gas flame holes 24 a, which may be positioned on acircular shape pattern substantially around the center of the flamestabilizing zone.

The second auxiliary combustible gas flame holes 24 b may be arranged toaccelerate the swirling flow substantially tangentially to the innercircumferential surface of the flame stabilizing zone. Alternatively,this design may be combined with the configuration shown in FIGS. 13,14, and 15 for ejecting the secondary auxiliary combustible gas slightlydownstream substantially tangentially to the inner circumferentialsurface of the flame stabilizing zone.

A second aspect of the present invention will be described below withreference to FIGS. 16 through 24.

FIGS. 16, 17, and 18 show a third embodiment of the present invention. Afirst combustion chamber 11 a surrounded by a first furnace wall 10 a isconfronted by a first flame stabilizing zone 15 a, which is surroundedby a peripheral wall 13 a defined by an inner circumferential surface ofa first cylindrical body 12 a and closed by a plate 14. The firstcylindrical body 12 a is integrally formed with the plate 14.

In the plate 14, there are defined a plurality of (four as shown) wastegas chambers 20 for holding and guiding a waste gas A to be treatedwhich is mainly composed of nitrogen and contains a deposition gascontaining SiH₄ and a halogen-base gas emitted from a semiconductorfabrication facility, for example, and a plurality of (four as shown)first auxiliary combustible gas chambers 21 a for holding and guiding aprimary auxiliary combustible gas B1, which is a fuel gas such ashydrogen, a town gas, LPG, etc. An air chamber 22 for holding andguiding air C is defined in the first cylindrical body 12 a, whichextends from the plate 14. The peripheral wall 13 a of the firstcylindrical body 12 a has an inside diameter which is substantially thesame as the inside diameter of a peripheral wall 10 a of the firstcombustion chamber 11 a, and is joined to the peripheral wall 10 a. Asecond flame stabilizing zone 15 b surrounded by a second peripheralwall 13 b which is defined by an inner circumferential surface of asecond cylindrical body 12 b is disposed axially downstream of the firstcombustion chamber 11 a.

The second cylindrical body 12 b has a second auxiliary combustible gaschamber 21 b defined therein for holding and guiding a secondaryauxiliary combustible gas B2, which is a fuel gas. The peripheral wall13 b of the second cylindrical body 12 b has an inside diameter which issubstantially the same as the inside diameter of the peripheral wall 10a of the first combustion chamber 11 a.

The peripheral wall of the second cylindrical body 12 b extends axiallydownstream and is joined to a peripheral wall 10 b of a secondcombustion chamber 11 b which has an inside diameter that issubstantially the same as the inside diameter of the peripheral wall ofthe second cylindrical body 12 b. A combustion gas outlet 30 isintegrally joined to the lower end of the combustion chamber 11 b.

The plate 14 has, defined in a lower surface thereof, a plurality of(four as shown) waste gas flame holes 23 extending from the waste gaschambers 20 and opening toward the first flame stabilizing zone 15 a,the waste gas flame holes 23 being smaller in diameter than the flamestabilizing zone 15 a, and a plurality of (four as shown) firstauxiliary combustible gas flame holes 24 providing communication betweenthe first auxiliary combustible gas chambers 21 a and the flamestabilizing zone 15 a, the waste gas flame holes 23 and the firstauxiliary combustible gas flame holes 24 being arranged in adoughnut-shaped pattern. The doughnut-shaped pattern means that thefirst auxiliary combustible gas flame holes 24 are disposed adjacent tothe waste gas flame holes 23 in a substantially annular shapesubstantially around the center of the plate that defines the flamestabilizing zone. In the present embodiment, the waste gas flame holes23 and the first auxiliary combustible gas flame holes 24 are positionedalternatively with each other, and the annular shape is in same positionwith a free vortex region where a swirling air flow has a high speed, asdescribed later on.

The inner peripheral wall 13 of the first cylindrical body 12 a has aplurality of (four as shown) air ejection nozzles 25 positioned awayfrom the plate and close to the first combustion chamber 11 a andproviding communication between the air chamber 22 and the flamestabilizing zone 15. The peripheral wall 13 b of the second auxiliarycombustible gas chamber 21 b has a plurality of (four as shown) secondauxiliary combustible gas flame holes 26 providing communication betweenthe second flame stabilizing zone 15 b and the second auxiliarycombustible gas chamber 21 b. The air ejection nozzles 25 extendsubstantially tangentially to the circumferential surface of the firstflame stabilizing zone 15 a for producing and ejecting a swirling flowof air C substantially circumferentially toward the first flamestabilizing zone 15 a. The second auxiliary combustible gas flame holes26 are arranged to eject a secondary auxiliary combustible gas B2 towardthe center of the second flame stabilizing zone 15 b.

Operation of the present embodiment will be described below.

The air C is guided into and held by the air chamber 22, and ejectedsubstantially circumferentially as a strong swirling flow from the airejection nozzles 25 defined in the inner circumferential surface of thefirst cylindrical body 12 a into the first flame stabilizing zone 15 a.The waste gas A is guided into and held by the waste gas chambers 20,and ejected from the waste gas flame holes 23 defined in the lowersurface of the plate 14 into the first flame stabilizing zone 15 a. Theprimary auxiliary combustible gas B1 is guided into and held by thefirst auxiliary combustible gas chambers 21 a, and ejected from thefirst auxiliary combustible gas flame holes 24 defined in the lowersurface of the plate 14 into the first flame stabilizing zone 15 a. Thewaste gas A and the primary auxiliary combustible gas B1 which areejected, are mixed with the swirling air flow. When ignited by anignition source, not shown, the mixed gases produce swirling flames,which are primary flames, along the inner circumferential surface of thefirst cylindrical body 12 a. The flow rate of the air C is greater thana theoretical equivalent to the flow rate of the primary auxiliarycombustible gas B1, so that the produced primary flames are fuel-leancombustion flames characterized by the lean fuel.

The air ejected substantially circumferentially from the peripheral wallproduces a strong swirling flow. The swirling flow has a vortex centerswirling together with the swirling flow and a doughnut-shape freevortex region around the vortex center with the flow speed being lowertoward the outer edge of the doughnut-shape free vortex. Since the flameholes for the waste gas A and the primary auxiliary combustible gas B1are defined in the lower surface of the plate 14 in an annular shape onsame position with a free vortex region, the waste gas A and the primaryauxiliary combustible gas B1 are ejected into the free vortex region andengulfed by the swirling air flow. These gases are sheared due tochanges in the speed of the swirling air flow, and sufficiently mixedwith the air C. The mixture of the waste gas A, the primary auxiliarycombustible gas B1, and the air C produces swirling fuel-lean flames andcauses a primary combustion. The flames produced in the first flamestabilizing zone 15 a complete the combustion in the first combustionchamber 11 a positioned downstream thereof. Although the primaryauxiliary combustible gas B1 and the air C are separately blown into thefirst flame stabilizing zone 15 a, since the waste gas is combustedafter it is mixed with the primary auxiliary combustible gas and theair, pre-mixed flames are produced.

Pre-mixed flames can be achieved when the waste gas A and the primaryauxiliary combustible gas B1 are ejected from positions on thedoughnut-shape pattern on the plate into the free vortex region wherethe swirling air flow has a high speed and is subject to large speedchanges, and are mixed with the air C, as is the case with the presentinvention. The swirling flow serves to hold the flames, allowing thecombustion to be maintained without the danger of extinguishing theflames even though the flames and fuel-lean. Generally, pre-mixedfuel-lean flames have a low combustion temperature and cause acombustion where the generated amount of NOx is low. Since pre-mixedflames produced in the first flame stabilizing zone 15 a are fuel-leanflames, they have a low combustion temperature and contains a low amountof NOx. The SiH₄ gas contained in the waste gas A is destroyed by way ofoxidization by the produced fuel-lean flames, producing a powder ofSiO₂. Since the primary fuel-lean flames start being produced from aposition spaced from the plate and the combustion is completed in thefirst combustion chamber 11 a, the SiH₄ gas contained in the waste gasstarts to be destroyed by way of oxidization from a position spaced fromthe plate, and converted in its entirety into the powder of SiO₂ in thefirst combustion chamber 11 a. If the powder of SiO₂ is exposed to ahigh temperature, it becomes a glassy substance and tends to adhere tothe peripheral wall 10 a. However, the powder of SiO₂ remains as apowder in the present embodiment because the fuel-lean flames have a lowtemperature.

In addition, the first flame stabilizing zone 15 a and the firstcombustion chamber 11 a are of substantially the same diameter,providing no stagnant regions in the flames and combustion exhaust gasflow. Because the speed of the axial downstream flow of the combustionexhaust gas is selected to blow away the powder of SiO₂, the producedpowder of SiO₂ is blown downstream by the flow of the combustion exhaustgas without being attached to the wall surfaces. As SiH₄ is destroyed byway of oxidization in a region spaced from the plate 14, the producedpowder of SiO₂ is prevented from being attached to and deposited on thesurfaces surrounding the waste gas flame holes 23 and the firstauxiliary combustible gas flame holes 24.

The primary combustion exhaust gas discharged after the combustion basedon the primary flames in the first combustion chamber 11 a is completedenters the second flame stabilizing zone 15 b. The secondary auxiliarycombustible gas B2 is ejected from the second auxiliary combustible gasflame holes 26 toward the center of the second flame stabilizing zone 15b. The ejected secondary auxiliary combustible gas B2 is mixed with theprimary combustion exhaust gas, causing a secondary combustion withoxygen remaining in the primary combustion exhaust gas. Flames producedin the second flame stabilizing zone 15 b complete the combustion withinthe second combustion chamber 11 b positioned downstream of the secondflame stabilizing zone 15 b. Since the concentration of the oxygenremaining in the primary combustion exhaust gas is much lower than theconcentration of oxygen contained in the air, a low-oxygen-concentrationcombustion takes place in the secondary combustion. In thelow-oxygen-concentration combustion, NOx is produced in a smallquantity, causing a low-NOx combustion. The low-NOx combustion iseffective to further increase the temperature of the primary combustionexhaust gas. A high temperature is required to thermally destroy ahalogen-base gas. In the present embodiment, the halogen-base gas can bethermally destroyed by produced higher-temperature flames in thesecondary combustion.

As described above, all the waste gas A is sufficiently mixed with theprimary auxiliary combustible gas B1 and the air C by the swirling airflow in the first flame stabilizing zone 15 a, producing primaryfuel-lean flames, and the fuel-lean swirling flames extending into firstcombustion chamber decompose the deposition gas of SiH₄ whilesuppressing the generation of NOx, and simultaneously blow away theproduced powder of SiO₂. In the second combustion chamber, ahigh-temperature combustion is caused with low oxygen, thermallydestructing the halogen-base gas in a low-NOx combustion.

Inasmuch as the primary and secondary auxiliary combustible gases B1, B2which are the fuel gas and the air C are mixed with each other in thefirst and second flame stabilizing zones, the primary and secondaryauxiliary combustible gases are not ignited in the first and secondauxiliary combustible gas chambers 21 a, 21 b, making the burner highlysafe, even if the first and second cylindrical bodies are heated by theflames. In the present embodiment, when the air C is suppliedcircumferentially to the air chamber 22, the air C swirls in the airchamber 22, uniformly cooling the air chamber 22 to prevent thecylindrical body from being heated. Similarly, when the secondaryauxiliary combustible gas B2 is supplied circumferentially to the secondauxiliary combustible gas chamber 21 b, the secondary auxiliarycombustible gas B2 swirls in the second auxiliary combustible gaschamber 21 b, uniformly cooling the second auxiliary combustible gaschamber 21 b.

In the third embodiment, the first cylindrical body 12 a and the secondcylindrical body 12 b, i.e., the first combustion chamber 11 a and thesecond combustion chamber 11 b, have substantially the same diameter aseach other. With this arrangement, the diameter of the swirling flowremains substantially the same to the outlet, eliminating any stagnantflow regions from the flame stabilizing zones to the outlet thereby toprevent the powder of SiO₂, which is generated when the deposition gasof SiH₄ is decomposed from being attached to the wall surfaces.

In the present embodiment, the burner has four air ejection nozzles 25defined in the circumferential surface. However, the burner may havemore than or less than four air ejection nozzles 25. Similarly, whilethe burner is shown as having four second auxiliary combustible gasflame holes 26 defined in the circumferential surface, the burner mayhave more than or less than four second auxiliary combustible gas flameholes 26.

FIGS. 19, 20, and 21 show a fourth embodiment of the present invention.The air chamber 22 defined in the first cylindrical body 12 a extends inthe axial direction of the peripheral wall 13 a of the first cylindricalbody 12 a. The air ejection nozzles 25 which provide communicationbetween the air chamber 22 and the first flame stabilizing zone 15 a areprovided in four at a group in a circumferential surface. Specifically,the air ejection nozzles 25 are provided in three groups including afirst group 25 a defined in the peripheral wall closely to the plate, asecond group 25 b defined in the peripheral wall, and a third group 25 cdefined in the peripheral wall at a position facing the combustionchamber. As with the third embodiment, the first group of air ejectionnozzles 25 is spaced from the plate 14 of the first cylindrical body 12a.

Operation of the present embodiment will be described below.

The air ejected from the air chamber 22 into the first flame stabilizingzone 15 a is divided into three groups spaced along the axial directionof the peripheral wall 13 a. Usually, the total amount of supplied airis several or several tens times the amount of auxiliary combustiblegas. When the air is divided into three stages along the axial directionand supplied to the first flame stabilizing zone 15 a, the amount of airejected from each of the groups is smaller than when the air is notdivided. The amount of air ejected from the air ejection nozzles 25 a inthe first group is not large enough to combust all the fuel gas,producing fuel-rich flames in the flame stabilizing zone. When air issupplied from the second and third groups of air ejection nozzles 25 b,25 c, the sufficient amount of air is supplied to the fuel gas,producing fuel-lean flames. When the air is thus supplied stepwise, thecombustion occurs slowly to prevent local high-temperature regions frombeing produced and to lower and uniformize the flame temperature in awide range, making the produced primary fuel-lean swirling flameselongate downstream. As a result, a low-NOx combustion is achieved, andSiH₄ is destroyed by way of oxidization slowly in a wide region. At thesame time, since a powder of SiO₂ is generated slowly, the removal ofthe powder of SiO₂ from the wall surfaces with the flame and thecombustion gas flow is further promoted.

In the present embodiment, the air ejection nozzles 25 are divided inthree groups along the axial direction of the flame stabilizing zone.However, the air ejection nozzles 25 may be divided in two groups orfour or more groups.

Not all the air ejection nozzles in the groups may eject the air toproduce a swirling flow toward the flame stabilizing zone. The airejection nozzles in the third group, for example, may eject air simplydownstream, rather than tangentially to the circumferential surface, ormay eject air toward the center of the flame stabilizing zone to causeturbulences with the waste gas and to be mixed with the waste gas.

In the present embodiment, the burner has two first auxiliarycombustible gas chambers 21 a and two auxiliary combustible gas flameholes 24, with the auxiliary combustible gas flame holes 24 beingdisposed between respective pairs of waste gas flame holes 23. With thisarrangement, the primary auxiliary combustible gas B1 is ejectedadjacent to the waste gas A and the mixing of the primary auxiliarycombustible gas B1 with the waste gas A is promoted.

FIG. 22 shows a fifth embodiment of the present invention. The secondauxiliary combustible gas chamber 21 b extends in the axial direction ofthe second cylindrical body 21 b. The second auxiliary combustible gasflame holes 26 providing communication between the second auxiliarycombustible gas chamber 21 b and the second flame stabilizing zone 15 bare provided in four at a group in a circumferential surface.Specifically, the second auxiliary combustible gas flame holes 26 areprovided in four groups including a first group 26 a defined in theperipheral wall in an upstream position, a second group 26 bsubstantially at the center in the longitudinal direction of theperipheral wall, and a third group 26 c defined in the peripheral wallat a position close to the combustion chamber.

Operation of the present embodiment will be described below.

The secondary auxiliary combustible gas B2 ejected from the secondauxiliary combustible gas chamber 21 b toward the second flamestabilizing zone 15 b is divided into three groups spaced along theaxial direction of the peripheral wall 13 b. When the secondaryauxiliary combustible gas B2 is divided into three stages along theaxial direction and supplied to the second flame stabilizing zone 15 b,the amount of secondary auxiliary combustible gas B2 ejected from eachof the flame holes is smaller than when the secondary auxiliarycombustible gas B2 is not divided, producing small flames in front ofthe flame holes. The secondary auxiliary combustible gas B2 is suppliedstepwise from the second auxiliary combustible gas flame holes 26 b, 26c in the second and third groups, producing low-oxygen flames that aresmaller stepwise downstream. Therefore, a high-temperature flame zone isproduced in a wide range over the second flame stabilizing zone 15 b andthe second combustion chamber 11 b. In this manner, a high-temperaturezone required to destroy the halogen-base gas is developed in a wideregion, increasing a high-temperature remaining time required to destroythe halogen-base gas for thereby destructing the halogen-base gas with ahigh efficiency.

In the present embodiment, the second auxiliary combustible gas flameholes 26 are divided in three groups along the axial direction of theflame stabilizing zone. However, the second auxiliary combustible gasflame holes 26 may be provided in two groups or four or more groups.

The second auxiliary combustible gas flame holes 26, 26 a, 26 b, 26 cmay not eject the secondary auxiliary combustible gas toward the centerof the flame stabilizing zone, but may eject the secondary auxiliarycombustible gas slightly downstream. Alternatively, the second auxiliarycombustible gas flame holes 26, 26 a, 26 b, 26 c may eject the secondaryauxiliary combustible gas to accelerate the swirling flow substantiallytangentially to the flame stabilizing zone, as with the air ejectionholes 25. Further alternatively, these optional arrangements may becombined with each other to eject the secondary auxiliary combustiblegas.

In the above embodiments, the burner may have a single first auxiliarycombustible gas flame hole 24, which may be disposed between either pairof waste gas flame holes 23. The burner may have two or three waste gasflame holes 23 rather than four waste gas flame holes 23. The burner mayhave a single waste gas flame hole 23 and a single first auxiliarycombustible gas flame hole 24, which may be positioned on a circularpattern substantially around the center of the first flame stabilizingzone. Further alternatively, the burner may have a single waste gasflame hole 23 and plural first auxiliary combustible gas flame holes 24,which may be positioned on a circular shape pattern substantially aroundthe center of the first flame stabilizing zone.

FIG. 23 shows a sixth embodiment of the present invention. The firstflame stabilizing zone 15 a and the first combustion chamber 11 a arepositioned successively downstream, the first combustion chamber 11 ahaving a lower portion bent into a U shape with an extension from whichthe second flame stabilizing zone 15 b, the second combustion chamber 11b, and a combustion exhaust gas outlet 30 a are successively arrangedupwardly. A draw off pipe 30 b for carrying away a powder of SiO₂ isconnected to the bottom of the U-shaped first combustion chamber. Withthis construction, the powder of SiO₂ which is produced in the firstcombustion chamber is separated from the exhaust gas in the U-shapedfirst combustion chamber, and drawn out of the combustion chamberthrough the draw off pipe 30 b without passage through the second flamestabilizing zone 15 b and the second combustion chamber 11 b.Consequently, the powder of SiO₂ is not deposited in the combustionchamber, but can be treated with increased efficiency.

FIG. 24 shows a seventh embodiment of the present invention. The firstcombustion chamber 11 a has a lower portion bent into an L shape with anextension from which the second flame stabilizing zone 15 b, the secondcombustion chamber 11 b, and the combustion exhaust gas outlet 30 a aresuccessively arranged horizontally. The draw pipe 30 b for carrying awaya powder of SiO₂ is connected to the bottom of the L-shaped firstcombustion chamber 11 a. With this construction, the powder of SiO₂which is produced in the first combustion chamber is separated from theexhaust gas in the L-shaped first combustion chamber, providing the sameadvantages as with the sixth embodiment.

A third aspect of the present invention will be described below withreference to FIGS. 25 through 27.

FIG. 25 shows an eighth embodiment of the present invention. Accordingto the eighth embodiment, a pipe or hole for directly viewing combustionflames is provided in the flame stabilizing zone or the combustionchamber upstream of the combustion flames, and a UV sensor for detectingthe combustion flames through the pipe or hole is provided. In theillustrated embodiment, the UV sensor is combined with thecombustion-type waste gas treatment system shown in FIG. 1. However, theUV sensor may be combined with the combustion-type waste gas treatmentsystem according to each of the above embodiments.

The combustion-type waste gas treatment system has a flame direct-visionpipe 31 for directly viewing combustion flames produced when the wastegas A, the auxiliary combustible gas B, and the air C are mixed andcombusted, thereby to confirm whether combustion flames are present ornot. As shown in FIG. 25, the flame direct-vision pipe 31 is positionedupstream of combustion flames, and an UV sensor 33 for detectingcombustion flames is connected through an optical fiber 32 to an end ofthe flame direct-vision pipe 31 remote from the combustion chamber. TheUV sensor 33 may alternatively be connected directly to the flamedirect-vision pipe 31.

Since the flame direct-vision pipe 31 is positioned upstream ofcombustion flames, rather than downstream of combustion flames,by-products such as dust generated when the exhaust gas is treated areprevented from clogging the light entrance port of the flamedirect-vision pipe 31, preventing the UV sensor 33 from failing todetect combustion flames. Since combustion flames are directly viewedthrough the flame direct-vision pipe 31, even when by-products having aUV absorbing capability are deposited in the reaction region (mainly inthe combustion chamber 11), they do not obstruct the introduction oflight, but the UV sensor 33 can detect combustion flames. Because theflame direct-vision pipe 31 is positioned in a wall upstream ofcombustion flames where the temperature is relatively low, the lightentrance port is not melted or corroded and closed at high temperatures.A quartz glass panel for passing ultraviolet radiation therethrough isdisposed in the junction between the flame direct-vision pipe 31 and theUV sensor 33, and a seal member is interposed between the quartz glasspanel and the junction, thus blocking the UV sensor 33 from theatmosphere in the combustion chamber 11. A purge gas inlet pipe 35 isconnected to the flame direct-vision pipe 31 for introducing a purge gas(PG: e.g., air) into the flame direct-vision pipe 31.

Inasmuch as the quartz glass panel is disposed in the junction betweenthe flame direct-vision pipe 31 and the UV sensor 33, and the purge gas(PG) is introduced into the flame direct-vision pipe 31, the lightentrance port of the flame direct-vision pipe 31 is prevented from beingclogged with by-products. The quartz glass panel is thick enough towithstand the internal pressure of the combustion chamber 11. The sealmember comprises a heat-resistant gasket. Light emitted from combustionflames in the flame direct-vision pipe 31 is transmitted to the UVsensor 33 by the optical fiber 32.

Since the light emitted from combustion flames in the flamedirect-vision pipe 31 is transmitted to the UV sensor 33 by the opticalfiber 32, the UV sensor 33 may be installed in a location free of spaceavailability problems and heat resistance problems even though the UVsensor 33 cannot be placed at the end of the flame direct-vision pipe 31remote from the combustion chamber due to such space availabilityproblems and heat resistance problems. For details of the layout of theflame direct-vision pipe and the UV sensor, reference should be made toJapanese patent application No. 2000-294632.

FIG. 26 shows a ninth embodiment of the present invention. According tothe ninth embodiment, a mixer outside of an auxiliary combustible agentsupply unit is supplied with an oxygen-containing gas from anoxygen-containing gas supply line and a fuel gas from a fuel gas supplyline, and mixes and supplies the gases to a combustion chamber, in whichthe supplied gases are combusted to produce combustion flames.

In the combustion-type waste gas treatment system, oxygen supplied froman oxygen gas supply line 40 and a fuel gas (e.g., propane gas) suppliedfrom a fuel gas supply line 41 are mixed with each other by a mixer 42,and the mixed gas is supplied from the mixer 42 through a mixed gas pipe43 to the auxiliary combustible gas chambers 21 of the waste gastreatment system. The mixed gas is then ejected from the auxiliarycombustible gas chambers 21 through the auxiliary combustible gasejection holes 24 into the flame stabilizing zone 15.

As described above, the mixer is positioned outside of the combustionchamber, and is supplied with the oxygen-containing gas and the fuelgas, and mixes and supplies the gases to the combustion chamber. It iseasy to adjust the mixing ratio of the oxygen-containing gas and thefuel gas in the mixer, allowing the waste gas to be combustedefficiently, preventing the mixed gas from being ignited abnormally andsuffering backfiring when it is ignited and extinguished. For details ofthe mixer, reference should be made to Japanese patent application No.2000-302410.

FIG. 27 shows a tenth embodiment of the present invention. According tothe tenth embodiment, the waste gas chamber houses therein a flow speedaccelerating means for increasing the flow speed of a combustible wastegas flowing through the waste gas chamber to a level equal to or higherthan the combustion velocity of the combustible waste gas.

The flow speed accelerating means has a slender pipe having a small pipediameter or an orifice 51 disposed in the waste gas chamber, and theinside diameter of the slender pipe or the orifice is selected such thatthe flow speed of the combustible waste gas passing through the slenderpipe or the orifice is equal to or higher than the combustion velocityof the combustible waste gas. The flow speed accelerating means isdisposed in a coupling mechanism, which couples a flange 52 on the inletof the waste gas chamber and a flange 53 on the end of a waste gassupply pipe, which supplies the waste gas to the inlet. The couplingmechanism comprises a clamp member 54, which tightens the outercircumferential edges of the flanges with a plate member having theorifice defined centrally therein and interposed between the flanges.The inside diameter of the orifice is preferably selected such that theflow speed of the combustible waste gas passing through the orifice isequal to or higher than the combustion velocity of the combustible wastegas.

The slender pipe 51 is disposed at the tip end of the waste gas chamberto increase the flow speed of the waste gas A for the purpose ofpreventing backfire into the waste gas chambers 20. The inside diameterd of the slender pipe 51 is selected such that the flow speed of thewaste gas A flowing through the slender pipe 51 is equal to or higherthan the combustion velocity of the waste gas A. Specifically, on theassumption that a hydrogen (H₂) gas whose combustion velocity is highestunder the same conditions flows in, the inside diameter d of the slenderpipe 51 is selected such that the flow speed is higher than thecombustion velocity, ranging from 2.5 to 2.8 m/s, of the hydrogen gas inthe air. For details of the flow speed accelerating means, referenceshould be made to Japanese patent application No. 2000-302410.

In the above embodiments, the burner is preferably made of a materialsuch as ceramics or a heat-resistant metal material. The auxiliarycombustible agent is not limited to a gas fuel such as hydrogen, towngas, or LPG, but may be a gas fuel or a liquid fuel containing oxygen ata concentration lower than the lower explosion concentration limit.

The flame stabilizing zone may not necessarily be of a cylindricalshape, but may be of a polygonal shape such as a rectangular shape. Theair ejected from the air ejection nozzles may behigh-oxygen-concentration air having an oxygen concentration higher than21%.

As described above, the first aspect of the present invention offers thefollowing advantages: Since the waste gas, the auxiliary combustibleagent, and the air are sufficiently mixed with each other and thencombusted, producing elongate flames, in the combustion chamber, thewaste gas can be combusted and destroyed with a high efficiency.Pre-mixed flames are produced to achieve a low-NOx combustion. If theair ejection nozzles are divided in a plurality of groups along theaxial direction of the flame stabilizing zone, then combustion flamesare further elongated for achieving a lower-NOx combustion andincreasing the efficiency with which to destroy the halogen-base wastegas.

The second aspect of the present invention offers the followingadvantages: The air, the auxiliary combustible gas, and the waste gaswhich is to be treated are sufficiently mixed with each other andcombusted to produce primary pre-mixed fuel-lean flames. Then, theauxiliary combustible gas is ejected from the second flame stabilizingzone to produce secondary high-temperature, low-oxygen flames. Thus,while a low-NOx combustion is being achieved, the deposition gascontaining SiH₄ and the halogen-base gas can simultaneously be destroyedwith a high efficiency.

If the air ejection nozzles are divided in a plurality of groups alongthe axial direction of the flame stabilizing zone, then the depositiongas containing SiH₄ can be destroyed slowly in a wide range. Since apowder of SiO₂ is also produced slowly, the removal of the powder ofSiO₂ with the flow of the combustion gas is further increased.

If the auxiliary combustible gas flame holes in the second flamestabilizing zone are divided in a plurality of groups along the axialdirection of the flame stabilizing zone, then a high-temperature regionrequired to decompose the halogen-base gas can be developed in a wideregion. Thus, the halogen-base gas can be destroyed with a highefficiency.

The third aspect of the present invention offers the followingadvantages: The pipe (hole) for directly viewing combustion flames isprovided upstream of the combustion flames, and the UV sensor isconnected to the pipe (hole) for monitoring the combustion flames stablyat all times. The mixer for mixing the oxygen-containing gas and thefuel gas with each other is disposed outside of the combustion chamber.The mixer allows the mixing ratio of the fuel gas to be adjusted withease, making it possible to combust the fuel gas efficiently.

The flow speed accelerating means for increasing the flow speed of thewaste gas to a level equal to or higher than the combustion velocity ofthe waste gas is effective to prevent backfire from occurring.

The burner for treating the waste gas according to the present inventionmixes the auxiliary combustible gas and the air with each other in theflame stabilizing zone. Therefore, the auxiliary combustible gas is notignited in the auxiliary combustible gas chamber even if the cylindricalbody is heated by the flames. Therefore, the burner is highly safe inoperation. As the air ejected from the air ejection holes produces aswirling flow in the flame stabilizing zone, it cools the surface of theperipheral wall of the cylindrical body to increase the heat-resistantservice life thereof.

Industrial Applicability

The present invention is useful in combusting and treating harmful wastegases such as a deposition gas containing SiH₄ and a halogen-base gas((CHF₃, C₂F₆, CF₄, etc.), which are emitted from semiconductormanufacturing system.

What is claimed is:
 1. A burner for treating a waste gas, characterizedin that: a flame stabilizing zone is open toward a combustion chamber,surrounded by a peripheral wall, and closed by a plate remotely fromsaid combustion chamber; a waste gas flame hole is disposed on saidplate for ejecting the waste gas toward said flame stabilizing zone; anauxiliary combustible gas flame hole is disposed on said plate forejecting the auxiliary combustible gas, and an air ejection nozzle isdisposed on the peripheral wall of said flame stabilizing zone forejecting air substantially circumferentially to produce a swirling flow;wherein said waste gas, an auxiliary combustible gas, and air areintroduced into and mixed with each other in said flame stabilizingzone, and the mixed gases are ejected toward said combustion chamberperpendicularly to said plate; said burner characterized in that: saidwaste gas flame hole and auxiliary combustible gas flame hole arearranged in a substantially circumferential pattern of an annular shapesubstantially around the center of said flame stabilizing zone; saidauxiliary combustible gas flame hole is disposed adjacent to said wastegas flame hole in said annular shape; and said annular shape is in sameposition with a free vortex region of said swirling flow.
 2. A burneraccording to claim 1, characterized in that said waste gas flame holehas a diameter smaller than inside diameter of said flame stabilizingzone.
 3. A burner according to claim 1, characterized in that a secondauxiliary combustible gas flame hole for ejecting the auxiliarycombustible gas is defined in the peripheral wall of said flamestabilizing zone downstream of said air ejection nozzle in an axialdirection of said flame stabilizing zone.
 4. A burner according to claim1, characterized in that said air ejection nozzle comprises air ejectionnozzles in a plurality of groups divided along the axial direction ofsaid flame stabilizing zone.
 5. A burner according to claim 1,characterized in that said flame stabilizing zone is of a cylindricalshape.
 6. A burner according to claim 5, characterized in that saidflame stabilizing zone and said combustion chamber are of a cylindricalshape and have substantially same diameter.
 7. A burner according toclaim 1, characterized in that a second flame stabilizing zone isdisposed downstream in the axial direction of said flame stabilizingzone, and has, defined in a peripheral wall thereof, a second auxiliarycombustible gas flame hole for ejecting a second auxiliary combustiblegas, and a combustion chamber is disposed downstream of said secondauxiliary combustible gas flame hole in an axial direction of saidsecond flame stabilizing zone.
 8. A burner according to claim 7,characterized in that said air ejection nozzle comprises air ejectionnozzles in a plurality of groups divided along the axial direction ofsaid first flame stabilizing zone.
 9. A burner according to claim 7,characterized in that said second auxiliary combustible gas flame holecomprises second auxiliary combustible gas flame hole in a plurality ofgroups divided along the axial direction of said second flamestabilizing zone.
 10. A burner according to claim 7, characterized inthat said first and second flame stabilizing zones and said combustionchambers are of a cylindrical shape and have substantially samediameter.
 11. A burner according to claim 1, characterized in that apipe or a hole for directly viewing combustion flames is disposedupstream of the combustion flames in said flame stabilizing zone or saidcombustion chamber, and a UV sensor is provided for detecting thecombustion flames through said pipe or said hole.
 12. A burner accordingto claim 1, characterized in that a mixer positioned outside of a supplyunit for the auxiliary combustible agent is provided for mixing anoxygen-containing gas from an oxygen-containing gas supply line and afuel gas from a fuel gas supply line, and supplying the gases to saidcombustion chamber, in which the supplied gases are combusted to producecombustion flames.
 13. A burner according to claim 1, characterized inthat a flow speed accelerating means is disposed in said waste gaschamber for increasing flow speed of a combustible waste gas to a levelequal to or higher than combustion speed of the combustible waste gas.